Most people who watch the History Channel’s “Ax Men” must cringe at the hazards faced by the loggers of northwest Oregon. With the snapped cables, falling trees and some swinging heavy equipment thrown into the mix, it’s no wonder that this is described as one of the most dangerous jobs in America.
When William Nash watches an episode of the series, he knows that something else will make him wince – the punishing environment for suspension systems. Logging equipment faces massive shifts in weight as timber is pulled on and off the vehicles, observes Nash, technical services manager for Hendrickson’s truck systems group.
Any suspension system that runs off road will be exposed to a steady pounding that comes with rocks and uneven terrain. And more than one on/off road driver has been known to lift axles once they hit an open highway, overloading other components in the process.
“In a generic sense, any vocational type of trailer always is going to be going through a rough road,” agrees Marty Watterson, customer service manager for ArvinMeritor’s North American trailer products group. But city delivery vehicles can face their own challenges as they climb curbs and twist their way through city intersections, he adds.
These trailer suspensions can require re-bushing in as little as three years, compared to the 10-year replacement cycles enjoyed by those who run over-the-road routes.
Regardless of the application, technicians who repair suspension components need to think of their work in the context of an entire system.
All too often, technicians will replace a worn component without thinking about the root cause of a failure. A vibrating driveline, for example, can be linked to a worn U-joint, but it also can be caused by an out-of-balance tube.
Someone who replaces a buckled bolster spring on an HN suspension may overlook the worn torque rod that led to the problem in the first place. And the replacement process for a failed beam and damaged cross tube on a Primaax suspension may overlook the other beam that was twisted when the cross tube fell to the ground.
If the systems share anything in common, it is the fact that the most helpful diagnostic tools will come in the form of reports that are submitted by drivers. A harsh ride, excessive noise or a lean in the vehicle can all indicate suspension-related challenges.
In the case of a dog-tracking trailer – especially one that will track to one side of the tractor, and later shift to the other side – an air-ride suspension may require re-bushing, while its mechanical counterpart may face a broken equalizer or spring, Watterson notes.
When reports of a harsh ride are linked to an air-ride suspension, meanwhile, the problem may be caused by lack of air in the air spring, Nash says. “We’ve even had cases where
